For manufacturing absorbent articles there are known the so-called "on line" processes, in which a continuous web is manufactured from which the article is cut out with as a segment of the desired length. These processes are typically employed for disposable articles such as baby diapers and feminine hygiene products. This kind of products incorporates cellulose fibres and superabsorbent polymers (SAP) either in fibre or powder form, that are blended up or arranged to form one of more layers, with the absorbent materials being sandwiched between sheets of tissue paper or the like, peripherally folded and bonded, or glued on such sheets and forming one or more layers. More particularly, in feminine hygiene products, SAP powders are bonded onto cellulose-based substrates (i.e. air-laid paper) and afterwards enveloped or wrapped by the substrates.
This process has the disadvantage of a limited width of the absorbent product, generally narrower than 600 mm, and of a poor flexibility since only a limited number of article configurations can be obtained. The number of layers in the absorbent article is limited, typically only one layer is provided when using SAP powders, and moreover such powders have to be encapsulated, which causes further technical restrictions.
Moreover, this known process is quite difficult to be modified to cope with future production requirements since even small modifications of the article involve substantial process changes with the associated high levels of investment and cost. Further, in many cases line modifications are unfeasible due either to existing space restraints or to the complexity of the employed process, or in case to a relative complexity of the desired product.
According to another known process, the absorbent article is manufactured through a separate (off line) process which delivers large sheets of laminated or composite material from which the desired absorbent articles are formed by slitting.
These composite or laminated sheets are formed from a large variety of components and/or materials. Typically, sheets of different materials such as, for example, tissue-paper and air-laid paper, nonwovens fabrics of different types, synthetic films and the like are joined together by thermal, chemical and/or mechanical bonding means. In case SAP materials are used, either as powders or fibres, they are evenly or randomly distributed over the supporting fabrics or included between them.
Although the so obtained products can have a considerable width (over 1,000 mm), nevertheless this kind of processn has other disadvantages.
More particularly, when such laminated products are further treated or slit down to form articles that are smaller or have particular configurations, their edges cannot be protected any longer, nor joined together for effectively retaining the powders or the fibres that can migrate in large amount out of the absorbing portion until reaching the external surface of the finished article, which renders the products totally unacceptable for sanitary purpose and in the food industry.
Furthermore, all of these processes have a reduced absorbing capacity, particularly when SAP materials in fibre, granule or powder form are used. As it is well known, these materials exhibit their highest absorbency in a loose condition, i.e. when they are neither made adhered to supporting sheets, nor compressed by a calendering. On the other hand the absorbent materials must remain in their designated areas of use, which requires a certain degree of fixing or bonding between the materials and the substrates. The two requirements are conflicting with each other, so that the products (and the articles) presently obtained by the known processes are in general unsatisfactory, the more so when SAP materials are being used.